Method for making a low ohmic pressure-contact electrical connection between split ring electrode and lead wire

ABSTRACT

A method for attaching a split ring electrode to a catheter tip section includes providing a tubing with a lumen and an opening in the tubing side wall, passing an electrode lead wire through the opening, and wrapping the lead wire around the tubing. A split ring electrode is mounted on the tubing over the wrapped lead wire and opening, with electrically-conductive thermoplastic elastomeric adhesive applied between the ring electrode and the outer surface of the tubing, and reheated to reflow.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of, and claims priority to and thebenefit of, U.S. patent application Ser. No. 13/802,259 filed Mar. 13,2013, now U.S. Pat. No. 9,278,187, the entire content of which isincorporated herein by reference.

FIELD OF INVENTION

This invention relates to electrophysiology catheters and, inparticular, to an improved method for attaching ring electrodes to thetip section of an electrophysiology catheter shaft.

BACKGROUND OF INVENTION

Electrophysiology catheters have been in common use in medical practicefor many years. They are used to map and stimulate electrical activityin the heart and to ablate sites of aberrant electrical activity. Amongthe various types of electrodes used in constructing electrophysiologycatheters are ring electrodes. These are metal rings positioned atvarious intervals along the length of the tip section. The ringelectrodes are electrically connected, via electrode lead wires whichextend through a lumen in the catheter, to electrical instruments, e.g.,a monitor, stimulator or source of energy, e.g., RF energy, forablation.

A conventional method for making the electrical connection between anelectrode lead wire and a ring electrode is to draw the electric leadwire out of a lumen in the tip section through an exit hole that extendsfrom the lumen to the side surface of the shaft of the catheter tip. Thedistal end of the electrode lead wire, stripped of any non-conductivecoating, is then welded or soldered onto the inner surface of a ringelectrode. The ring electrode is then slipped over the tip shaft to aposition directly over the exit hole while drawing the electrode leadwire back into the lumen. The ring electrode is then secured in place,e.g., by swaging or by the application of an appropriate adhesive. Aresin, e.g., polyurethane resin, is often applied to the margins oredges of the ring electrode to assure a smooth transition between theouter circumferential surface of the ring electrode and the outercircumferential surface of the catheter shaft.

Conventional methods for mounting ring electrodes on a catheter havecertain drawbacks. For example, because the electrode lead wire must bedrawn back into the lumen of the catheter tip section as the ring isslipped over the shaft of the tip section, the exit hole cannot besealed and visually inspected before the ring electrode is swaged orglued over the exit hole. Further, the ring electrode must have asufficiently larger diameter than that of the shaft of the catheter tipto slide over the shaft to its final position. Stretching the shaft ofthe tip section to reduce its diameter is one technique that allows theuse of a closer fitting ring electrode. This technique, however, isoperator dependent and tends to lead to inconsistent quality in theplacement of the ring electrode on the shaft. Further, ring electrodesmounted by the conventional method tend to “pull away” from the shaft ofthe tip section, i.e., the edge of the ring electrode tends to separatefrom the surface of the catheter tip shaft along the outside of thecurve, during tight bending of the tip section.

Other methods include laser welding, for example, laser melting througha ring electrode to create a laser-welded low ohmic electricalconnection to a lead wire. Laser welding however relies on accuratelocation of the lead wire under the ring electrode during welding. Likeconventional resistance welding of ring electrodes, laser welding ismanual labor intensive and time-consuming operation that is prone toelectrical defects due to improper workmanship methods. Moreover, sincecatheter tubing is pierced with holes to pass the lead wire from a lumento outside the tubing, the holes must be made fluid tight after ringplacement over the tubing.

Another method is disclosed in US Publication 2005/0097737 A1. Therein,a ring electrode with a flared skirt is swaged to reduce its inner andouter diameter so that it is tightly secured to a tip shaft and makessufficient pressure contact with underlying electrode lead wire toprovide a low ohmic connection. Although the process eliminates ringresistance welding, the low ohmic connections may not be stable longterm due to the tendency for stress relaxation of the tubing elastomericmaterial.

For these and other reasons, there is a need to find a method forattaching ring electrodes to the shaft of the catheter tip section thatis less costly, more efficient and does not exhibit the above mentioneddrawbacks and disadvantages of the conventional method.

SUMMARY OF THE INVENTION

The present invention provides a method for attaching a ring electrodeto the tubing of a catheter tip section. The method comprises providinga tubing with at least one lumen, a side wall and at least one openingin the side wall providing communication between the lumen and outsidethe tubing. An electrode lead wire is passed through the lumen and outof the opening to expose a distal portion of the electrode lead wirewhich is positioned or wrapped around on an outer surface of the tubing.A split ring electrode is on the outer surface of the tubing coveringthe opening and the distal portion of the lead wire, with anelectrically-conductive adhesive being provided between the ringelectrode and the outer surface of the tubing.

In one embodiment, the electrically-conductive themoplastic elastomericadhesive is applied as a film on an inner surface of the split ringelectrode before mounting on the outer surface of the tubing.

In another embodiment, the electrically-conductive adhesive is appliedonto the outer surface of the tubing, covering the opening and at leasta portion of the distal portion of the lead wire before mounting thesplit ring electrode.

In a detailed embodiment, the ring electrode comprises a platinum alloy,for example, an alloy comprising platinum and at least one from thegroup consisting of iridium, palladium and copper. In a more detailedembodiment, the platinum alloy comprises about 90% platinum.

In a detailed embodiment, the lead wire comprises, stainless steel,copper and/or nickel alloy. The lead wire may comprise a coating ofsilver, for example a silver flash coating with a thickness rangingbetween about 20-30 microns. The lead wire may have a diameter rangingbetween about 0.002 inch and 0.005 inch, and preferably between about0.002 inch and 0.003 inch. The distal portion of the electrode lead wiremay be wrapped about two full turns distally on an outer surface of thetubing.

In a detailed embodiment, the electrically-conductive adhesive comprisesan electrically-conductive phase change thermal bonding adhesive, andthe method of the present invention includes heating theelectrically-conductive adhesive to reflow.

In a detailed embodiment, the split ring electrode has a width rangingbetween about 1.0 and 3.0 mm and a thickness between 0.001-0.003 inches.The split ring electrode may be constructed of a low cost copper orbrass 260 base material with an outer coating of gold, platinum orpalladium to prevent oxidization. The thickness of the coating may rangebetween about 10 and 50 microns, and preferably between about 20 and 40microns.

The method of the present invention may include using a split dieassembly with a first and second heated forming die members utilized toradially compress the split ring electrode onto the outer surface of thetubing. Heat may be applied during radial compression to melt theelectrically-conductive phase change thermal bonding adhesive so itbonds to both the tubing surface and the lead wires.

The method of the present invention provides many advantages includingthe following:

-   -   1) Much smaller tensile strength lead wires can be used because        the wire resistance per unit length is reduced due to a highly        conductive (electrically) silver plated outer coating. This        allows fitting more lead wires per lumen fixed cross sectional        area. Thus higher density electrodes and/or smaller tip French        sizes may be utilized with this design.    -   2) Micro-silver particles in the electrically-conductive        adhesive and the silver flash coating on stainless steel, copper        or nickel alloy lead wires create a flexible low ohmic        electrical connection regardless if silver has oxidized on the        lead wires or in the coating. The adhesive is an elastomer so it        remains flexible as with the tip section tubing. When the        catheter tip section is deflected, no stress is built up between        the elastomeric adhesive interface and the tip material and        split ring electrode.    -   3) A unique characteristic of thermal bonding adhesive is its        ability to be easily reworked. Merely heating the adhesive past        its phase-change temperature (about 250° F.) allows a mounted        split ring electrode to be removed or replaced. The adhesive can        be heated past its phase=change temperature numerous times        allowing for multiple re-works/repairs as necessary. Catheters        with failed split ring electrode electrical connection can be        repaired without being discarded.    -   4) Multiple hot melt adhesive coated split rings electrodes can        be mounted in a one-step 50 second thermal bonding process. The        requirement to slip on a full ring electrode and slide into        place on the tubing is eliminated.    -   5) Method of invention facilitates manufacture of high-density        ring electrode catheters where the lead wire diameter is        minimized by plating with conductive silver to reduce catheter        French size. Silver is one of the most electrically conductive        elements even when oxidized. Thus the addition of silver plating        on the outside of a low conductivity wire greatly reduces the        wire's resistance per unit length.    -   6) Reflow temperature of electrically conductive thermal bonding        adhesive can be adjusted depending on formulation and material        melt temperature of tubing for optimizing adhesive bonding and        provide ring electrodes that are partially embedded in the        tubing material so the ring electrodes are flush with the outer        surface of the tubing.    -   7) Split ring electrodes may be die cut from a large sheet of        material and thus they are more economical to manufacture than        full ring electrodes.    -   8) Thermal bonding adhesive and tubing material are both        elastomers with similar mechanical properties. During heating        and cooling cycles, both have similar expansion coefficients and        thus grow and shrink comparably thus maintaining a consistent        low ohmic electrical connection.    -   9) The reflow process of the thermal bonding adhesive makes each        split ring electrode self-sealing at the lead wire exit hole.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a side, exploded view of a portion of a catheter tip sectionwith an exit hole and an electrode lead wire extending out of the exithole, and a split ring electrode, in accordance with an embodiment ofthe present invention.

FIG. 2A is a side view of a catheter tip section with a mounted splitring electrode partially broken away, in accordance with an embodimentof the present invention.

FIG. 2B is a side view of the catheter tip of FIG. 2A, with no partsbroken away.

FIG. 2C is an end cross-sectional view of the catheter tip section ofFIG. 2A, taken along line C-C.

FIG. 2D is an end cross-sectional view of a catheter tip section with amulti-lumened tubing, in accordance with an embodiment of the presentinvention.

FIG. 3A is an opposing side view of the catheter tip section of FIG. 2A,with the mounted split ring electrode partially broken away.

FIG. 3B is a side view of the catheter tip section of FIG. 3A, with noparts broken away.

FIG. 4 is a perspective view of an split ring electrode in its initialform prior to mounting.

FIG. 5 is a schematic perspective view of a die assembly in use on oneembodiment of a catheter tip section in accordance with a feature of thepresent invention.

FIG. 6 is a schematic perspective view of a dispensing needle applyingadhesive to a catheter tip section in accordance with an embodiment ofthe present invention.

FIG. 7 is a side view of the catheter tip section of FIG. 6 prepared formounting of split ring electrodes.

FIG. 8 is a schematic perspective view of a die assembly in use onanother embodiment of a catheter tip section in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, there is provided an improvedmethod for attaching a split ring electrode to a catheter shaft formaking a low ohmic connection to an electrode lead wire using anelectrically-conductive adhesive, including an electrically-conductivephase-change thermal bonding adhesive. The method is applicable tocatheters of any size and only requires that the body to which the splitring electrode is attached has a generally circular cross-section and atleast one lumen therethrough for passage of an electrode lead wire.

The method comprises first providing a distal tip section of a catheterhaving at least one lumen extending longitudinally through at least aportion of the tip section. The tip section may be the distal portion ofan integral, elongated catheter body or may be a separate structure thatis attached to the distal end of the catheter body as is well known inthe art. See, for example, U.S. Pat. No. 6,171,277, which isincorporated herein by reference. The catheter body and tip section maybe made of any material suitable for use in the construction ofelectrophysiology catheters. Polyurethane is an example of a suitablematerial.

With reference to FIGS. 1 and 2A-2C, a tubing or shaft 10 of the distaltip section comprises a lumen 12 and a small exit hole 14 that extendsbetween the lumen 12 and the outer side surface of the tubing 10. Thesize of the exit hole 14 is not critical and can be formed, for example,by inserting a needle through the wall of the tubing 10 and heating theneedle sufficiently to form a permanent hole. Such an exit hole issufficiently large to enable an electrode lead wire 16 to be pulledthrough the hole, e.g., by a microhook or the like, and yet sufficientlysmall to be easily sealed.

The electrode lead wire 16 is pulled through the lumen 12 of the tipsection 10 and out of the exit hole 14. The length of the electrode leadwire 16 that extends out of the exit hole 14 is not critical, but issufficient to allow the electrode lead wire 16 to be wrapped around thetubing 10 of the tip section 10 a desired number of turn(s). Theelectrode lead wire 16 may be made of any suitable, preferablynon-oxidizing, material and may have any suitable diameter. In oneembodiment, the electrode lead wire is about 0.002 inch diameter wire ofstainless steel, copper and/or a nickel alloy, for example, a nickelalloy comprising up to about 67% nickel, with the remainder beingcopper, iron and/or other trace elements. A suitable nickel alloy isMONEL 400 binary alloy of equal proportions of nickel and copper,available from Special Metals Corporation of New Hartford, New York. Ina preferred embodiment, a MONEL 400 lead wire has a flash coating ofsilver of a thickness ranging between about 20-30 microns.

The portion of the electrode lead wire 16 that extends out of the exithole 14 is stripped of insulation and wrapped around the tubing 10. Aparticularly preferred wrapping technique is shown in FIG. 1. In thistechnique, the electrode lead wire 16 extending from the exit hole 14 iswrapped around the tubing 10 in one direction for two full turns, withthe two turns proceeding in a distal direction. The free end of theelectrode lead wire 16 is passed under the two wraps in a clove hitcharrangement, as shown. After wrapping, the free end of the electrodelead wire 16 is pulled to eliminate any slack in the wraps. Distal endof the lead wire 16 is trimmed adjacent to the lead wire wrap.

With additional reference to FIGS. 3A and 3B, a split ring electrode 22is provided which has an inner diameter slightly greater than the outerdiameter of the tubing 10 to allow it to be slipped over the tubing 10to a location over the wrapped electrode lead wire 16 and exit hole 14.For example, if the tubing 10 has an outer diameter of 0.084 inch, aring electrode 22 having an inner diameter of 0.085 inch is preferred.

As shown in FIG. 4, the ring electrode 22 is formed from an elongatedrectangular planar piece of material 25 with an outer surface 24 and aninner surface 26 an two opposing ends 27. The ring electrode may be madeof any suitable conductive, preferably non-oxidizing, material. Onepreferred material is a platinum-based alloy including iridium and/orpalladium. In one embodiment, the alloy includes about 90% platinum,with the remainder being iridium and/or palladium. The alloy has a widthranging between about 1.0 and 3.0 mm. If a non-noble metal is used asthe base material (copper or brass 260) for the split ring electrode, aplating 47 of gold or palladium with a thickness ranging between about10 and 40 microns is provided on the inner and outer surfaces 24 and 26.Polyurethane adhesive may be used to coat and seal both distal andproximal circumferential edges 31D and 31P (FIG. 4).

On the inner surface 26 the ring electrode 22 has a coating of anelectrically-conductive adhesive 17, including anelectrically-conductive-phase-change thermal bonding adhesive in filmform 28. A suitable adhesive is FASTELEK available from FastelAdhesives, San Clemente, Calif. FASTELEK is an electrically conductiveEVA-based solvent free (metallic filled) adhesive that is available as afilm and designed to provide low resistance electrical conductivity,uniform adhesion and sealing across a desired material interface.FASTELEK is available in multiple fillers (silver, nickel or gold),thicknesses and phase-change (melt point) temperatures. FASTELEK is anelastomeric adhesive with about a shore 80-90 A hardness and 150%tensile elongation before failure and is designed to adhere strongly toa wide range of metals, plastics and elastomers.

The ring electrode 22 is positioned over the wrapped lead wire 16 withthe outer surface 24 facing away from the tubing 10 and the thermalbonding adhesive film 28 facing the wrapped lead wire 16, with a lengthdimension of the ring electrode generally perpendicular to thelongitudinal axis of the tubing 10. Heat and acircumferentially-compressive force are applied to wrap, adhere, mountand electrically connect the ring electrode 22 around the tubing 10. Thering electrode 22 covers the wrapped lead wire 16 with the wrapped leadwire being generally centered under the ring electrode. Mounted on thetubing 10, the ring electrode adopts a C cross-sectional shape with theends 27 approaching each other around the tubing 10 forming a split orgap 29 in the C-shape. Notably, the ring electrode 22 is oriented on thetubing 10 such that the split 29 avoids the exit hole 14 where the leadwire 16 exits the lumen 12. In the illustrated embodiment, the split 29and the exit hole 14 are diametrically opposite of each other.

With the application of heat, the thermal bonding adhesive film 28begins its controlled flow when cycled past its phase-change temperatureand bonds to the silver flash-plated lead wire 16 under the ringelectrode 22 and filling in and adjusting any microscopic surfaceconditions or irregularities that may exist on the outer surface of thetubing 10. As such, the adhesive film 28 reflows to seal voids and airgaps between the ring electrode 22 and outer surface of the tubing 10,including the hole 14 sealing it and protecting the lumen 12 fromcontamination that can otherwise enter the lumen 12 through the hole 14.The adhesive film 28 also reflows to seal circumferential edges ondistal and proximal edges 31D and 31P of the ring electrode 22. Theadhesive film 28 further flows into the gap 29 thereby sealingtransverse edges at ends 27.

The film 28 may be produced by heating the adhesive to flow onto a largesheet of foil, with a thickness of 0.0007 inch, and die cut from thelarge sheet of foil. During the mounting of the split ring electrode 22to the tube 10, the adhesive film 28 is reheated for reflowing to attachit to the tubing and lead wire.

As illustrated in FIG. 2C, the distal tip section 15 manufactured inaccordance with the present invention has a C-shaped split ringelectrode 22 mounted on the tubing 10 which has the lumen 12 and theopening 14 through which the lead wire 16 passes from the lumen 12 to anouter surface of the tubing around which a distal portion of the leadwire is wrapped. The split ring electrode 22 and the lead wire 16 areelectrically connected by the thermal bonding adhesive film 28 betweenan outer surface of the tubing 10 and the ring electrode 22 which ismounted on the tubing 10 covering the wrapped lead wire 16. Theelectrical connection is advantageously accomplished without resistancewelding or laser welding. Accordingly, manufacture of a distal tipsection 15 under the present invention is less manual-labor intensive,less time-consuming and less prone to electrical defects due to improperworkmanship methods. It is understood that the present inventionincludes the use of a multi-lumened tubing 10′ as shown in FIG. 2D,where the lead wires 16 extend through a lumen 12′ in communication withthe openings 14.

Once the ring electrode 22 has been positioned directly over the wrappedlead wire 16, the distal tip section 15 (and any other portion of thecatheter carrying split ring electrodes) is placed in a die assembly 30,as shown in FIG. 5. Each of movable upper and lower semi-circular shapeddie half members 32 has semi-cylindrical recessed form 34 which jointlyform a full cylindrical form with a diameter that defines the desiredouter diameter size for the distal tip section 15 (and any other portionof the catheter carrying split ring electrodes). Each of the upper andlower die members 32 may be heated so as to melt and reflow the thermalbonding adhesive film 28 which allows the reflowed adhesive to bond withthe wrapped lead wire 16 and ring electrode 22 and tubing 10. The diemembers 32 may be heated by any conventional methods, e.g., it may beheated by an electric heating element. Alternatively or in addition, hotair may be supplied by a tube or pipe 36 as shown. As described above,the reflowed adhesive also fills in microscopic surface conditions,adjusts for any surface irregularities in the tubing 10 outsidediameter, fills in the exit hole 14 and seals proximal and distalcircumferential edges of the ring electrodes.

Accordingly, the reflowed adhesive forms electrically conductivelow-ohmic connection between the split ring electrodes 22 and theirrespective lead wires 16. To that end, the silver coating on the leadwires 16 greatly reduces the lead wire resistance per linear unit lengthwhere both lead wires 16 and thermal bonding adhesive contain silverwhich has the highest conductivity of any element, a flexible low ohmconnection is established without any mechanical stresses introduced inthe ring electrodes 22 or tubing 10. The split ring electrodes 22mounted in accordance with the present invention also has the benefit ofreduced resistance between the ring electrode 22 and connector pins (notshown) in a catheter control handle 16 by about 50% compared to existingcatheters using MONEL lead wires. MONEL 400 wire at 0.003 inches indiameter has a resistance of 40 ohms per foot and flash silver platedMONEL 400 at 0.002 inches in diameter has a reduced resistance of 20ohms per foot. Accordingly, the present invention facilitates themanufacture of very economical, high-density electrode catheters sinceall ring electrodes can be located on the distal tip section andelectrically connected to lead wires in a single operation and MONELlead wires with flash silver coating can be made in smaller diameterswhile decreasing the overall ring electrode to connector pin resistance.The number of lead wires (e.g., from 1 to 50+) that be fed through alumen can also be increased.

It is understood that the local area of the tubing 10 adjacent thewrapped lead wires is heated while the distal tip section 15 is in thedie assembly. Where the tubing is of polyurethane, a temperature betweenabout 110-125 C also softens material of tubing. This softening may helpto embed the wrapped lead wires into the outer surface of the tubing soas to allow the die assembly to further minimize the outer diameter ofthe ring electrode as mounted on the tubing over the wrapped lead wires.

It is understood that, while heating to facilitate embedding of the wirewraps is preferred, it is not necessary to practice the invention.Moreover, when heating is used, any temperature that softens the plasticmaterial of the shaft of the tip section may be employed. Further, anytechnique or device that allows heating, particularly localized heating,may be used.

An alternative method of manufacture in accordance with the presentinvention is illustrated in FIGS. 6-8. The tubing 10 is prepared withexit holes 14 and lead wires 16 wrapped around the outer surface of thetubing, as described above. The prepared tubing is then positioned undera dispensing needle 40 dispensing the thermal bond adhesive 17 directlyon the outer surface of the tubing 10 and the wrapped lead wires 16 asthe tubing 10 is rotated axially as shown by the arrow 45. The adhesivemay be applied as a continuous line or as individual beads 42. Thedispenser needle 40 is heated, e.g., by an electric heating element, tomelt and reflow the adhesive 17, or hot air may be provided via tube orpipe 36. A split ring electrode 22 (with or without a thermal bondadhesive film) is then mounted on the tubing 10 to cover the appliedadhesive 42 and the wrapped lead wire 16 by means of the die assembly30.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. For example, the advancing wire control mechanism may beintegrated anywhere along the control handle. User interface may bemodified to allow for a linear motion deflection knob rather than therotational knob mentioned above. If bi-directional deflection isdesired, a second puller wire may be provided, as understood by one ofordinary skill in the art. Moreover, the drawings are not necessarily toscale.

Accordingly, the foregoing description should not be read as pertainingonly to the precise structures described and illustrated in theaccompanying drawings, but rather should be read consistent with and assupport to the following claims which are to have their fullest and fairscope

What is claimed is:
 1. A method for attaching a split ring electrode toa tubing of a catheter, comprising: providing a tubing with at least onelumen, a side wall and at least one opening in the side wall providingcommunication between the at least one lumen and outside the tubing;passing an electrode lead wire through the at least one lumen and out ofthe at least one opening to expose a distal portion of the electrodelead wire; positioning the distal portion of the electrode lead wire onan outer surface of the tubing; mounting a split ring electrode on theouter surface of the tubing covering the opening and the distal portionof electrode lead wire; and providing an electrically-conductiveadhesive between the ring electrode and the outer surface of the tubing.2. The method of claim 1, wherein providing an electrically-conductiveadhesive includes applying a film of the electrically-conductiveadhesive on an inner surface of the split ring electrode before mountingon the outer surface of the tubing.
 3. The method of claim 2, whereinthe ring electrode comprises a platinum alloy.
 4. The method of claim 3,wherein the platinum alloy comprises platinum and at least one selectedfrom the group consisting of iridium, palladium and copper.
 5. Themethod of claim 3, wherein the platinum alloy comprises about 90%platinum.
 6. The method of claim 1, wherein the at least one lead wirecomprises, stainless steel, copper and/or nickel alloy.
 7. The method ofclaim 1, wherein the at least one lead wire comprises a coating ofsilver.
 8. The method of claim 3, wherein the coating of silver has athickness ranging between about 20-30 microns.
 9. The method of claim 1,wherein the lead wire has a diameter ranging between about 0.002 inchand 0.005 inch.
 10. The method of claim 1, wherein providing anelectrically-conductive adhesive includes applying theelectrically-conductive adhesive on at least portions of the distalportion of the electrode and of the outer surface before mounting thesplit ring electrode.
 11. The method of claim 10, wherein theelectrically-conductive adhesive is applied as a generally continuousline circumferentially around the tubing.
 12. The method of claim 10,wherein the electrically-conductive adhesive is applied as individualbeads circumferentially around the tubing.
 13. The method of claim 1,wherein positioning the distal portion of the electrode lead wire on anouter surface of the tubing includes wrapping the distal portion aroundthe outer surface of the tubing.
 14. The method of claim 1, wherein theelectrically-conductive adhesive comprises an electrically-conductivephase change thermal bonding adhesive.
 15. The method of claim 1,wherein further comprising heating the electrically-conductive adhesiveto reflow.
 16. The method of claim 1, wherein the split ring electrodehas a thickness ranging between about 1.0 and 3.0 mm.
 17. The method ofclaim 1, wherein the split ring electrode has a coating of gold orpalladium.
 18. The method of claim 17, wherein the coating on the splitring electrode has a thickness ranging between about 10 and 40 microns.19. The method of claim 1, wherein mounting a split ring electrode onthe outer surface of the tubing comprises radially compressing the splitring electrode onto the outer surface of the tubing.
 20. The method ofclaim 1, wherein mounting a split ring electrode on the outer surface ofthe tubing comprises radially compressing the split ring electrode ontothe outer surface of the tubing and heating the electrically-conductiveadhesive.